Co-planar surface and torsion device mirror structure and method of manufacture for optical displays

ABSTRACT

A spatial light modulator is provided. The spatial light modulator includes a first substrate comprising a plurality of electrically activated electrodes and a bias grid and a standoff structure coupled to the first substrate. The standoff structure includes a central portion projecting to a first height above the first substrate and an extension portion projecting to a second height above the first substrate, the second height being less than the first height. The spatial light modulator also includes a mirror plate comprising a central contact structure integrally formed with the central portion of the standoff structure, a torsion beam coplanar with the central contact structure and free from contact with the standoff structure, and a reflective surface coupled to the plurality of torsion arms and free from contact with the standoff structure.

CROSS-REFERENCES TO RELATED APPLICATIONS

The following two regular U.S. patent applications (including this one)are being filed concurrently, and the entire disclosure of the otherapplication is incorporated by reference into this application for allpurposes.

U.S. application Ser. No. ______; filed ______, entitled “Co-PlanarSurface and Torsion Device Mirror Structure and Method of Manufacturefor Optical Displays” (Attorney Docket No. 021713-003700US); and

U.S. application Ser. No. ______; filed ______, entitled “Method andDevice for Fabricating a Release Structure to Facilitate Bonding ofMirror Devices onto a Substrate” (Attorney Docket No. 021713-003800US).

BACKGROUND OF THE INVENTION

This present invention relates generally to manufacturing objects. Moreparticularly, the invention relates to a method and structure forfabricating a spatial light modulator with a co-planar surface andtorsion device. Merely by way of example, the invention has been appliedto the formation of a spatial light modulator having a torsion springand mirror plate positioned in the same plane. The method and device canbe applied to spatial light modulators as well as other devices, forexample, micro-electromechanical sensors, detectors, and displays.

Micro-electromechanical systems (MEMS) are used in a number ofapplication areas. For example, MEMS have been used in micro-mirrorarrays, sensors, and actuators. In some of these applications, asuspended member is supported by a flexible hinge attached to astationary portion of the mirco-mirror array. Flexibly attached to thehinge, the suspended member is attracted to an electrode uponapplication of an electrical force and restored to an original positionby a restoring force. In this manner, the array of micro-mirrors can betilted in relation to a light source. In some applications, it isbeneficial to have the hinge located beneath the micro-mirror surface ina hidden position, enabling the fill factor of the array to beincreased. As the fill factor of the micro-mirror array is increased,the potential quality of two-dimensional images created by opticalsystems using the array is improved.

As merely an example, some conventional MEMS have utilized variousmicro-mirror designs, such as micro-mirrors mounted on flexiblepedestals coupled to the backside of the micro-mirror surface. In someof these designs, the flexible pedestals extending from the mirrorsubstrate are bonded to a control substrate using a wafer bondingprocess. However, in these designs, the reliability and repeatability ofthe process of bonding the flexible posts to the control substrate maybe reduced due to the small surface areas joined during the bondingprocess. Thus, there is a need in the art for methods and apparatus foran improved support structure adapted to couple mirror devices to acontrol substrate.

SUMMARY OF THE INVENTION

According to the present invention, techniques for manufacturing objectsare provided. More particularly, the invention relates to a method andstructure for fabricating a spatial light modulator with a co-planarsurface and torsion device. Merely by way of example, the invention hasbeen applied to the formation of a spatial light modulator having atorsion spring and mirror plate positioned in the same plane. The methodand device can be applied to spatial light modulators as well as otherdevices, for example, micro-electromechanical sensors, detectors, anddisplays.

According to a specific embodiment of the present invention, a spatiallight modulator is provided. The spatial light modulator includes afirst substrate comprising a plurality of electrically activatedelectrodes and a bias grid. The spatial light modulator also includes astandoff structure coupled to the first substrate. The standoffstructure includes a central portion projecting to a first height abovethe first substrate and an extension portion projecting to a secondheight above the first substrate, the second height being less than thefirst height. The spatial light modulator also includes a mirror plateincluding a central contact structure integrally formed with the centralportion of the standoff structure, a torsion beam coplanar with thecentral contact structure and free from contact with the standoffstructure, and a reflective surface coupled to the torsion beam and freefrom contact with the standoff structure.

According to another specific embodiment of the present invention, amicro-mirror flexibly supported by a standoff structure is provided. Themicro-mirror includes a mirror layer having an upper surface adapted toreflect incident radiation and a lower surface opposite the uppersurface. The standoff structure includes a first portion integrallyformed with the mirror layer. The first portion includes a first planarinterface coupled to the lower surface of the mirror layer, a secondplanar interface opposite the first planar interface, and a body sectionextending along a first axis from the first planar interface to thesecond planar interface. The standoff structure further includes asecond portion extending along a second axis perpendicular to the firstaxis. The second portion includes an upper surface physically separatedfrom the plane of the first planar interface by a first distance, alower surface coplanar with the second planar interface, and a bodysection extending along the first axis. The micro-mirror also includes asubstrate coupled to the second planar interface of the first portion ofthe standoff structure and to the lower surface of the second portion ofthe standoff structure.

According to an alternative embodiment of the present invention, amethod of fabricating a spatial light modulator is provided. The methodincludes providing a first substrate structure comprising a plurality oflayers and forming a standoff structure in a first layer selected fromthe plurality of layers of the first substrate structure. The methodfurther includes providing a second substrate comprising a bondingsurface and a support surface and joining the standoff structure to thebonding surface of the second substrate. The method also includesremoving at least a second layer selected from the plurality of layersof the first substrate structure, selectively patterning the first layerof the first substrate structure to form a micro-mirror, and selectivelypatterning the first layer to remove a portion of the standoff structureand form a torsion spring hinge co-planar with the micro-mirror.

Many benefits are achieved by way of the present invention overconventional techniques. For example, the present technique provides aneasy to use process that relies upon conventional technology. In someembodiments, the method provides for a spatial light modulator with anincreased fill-factor. Additionally, the method provides a process thatis compatible with conventional process technology without substantialmodifications to conventional equipment and processes. Preferably, theinvention provides for an improved integrated structure includingintegrated circuits and mirror structures for display applications.Depending upon the embodiment, one or more of these benefits may beachieved. These and other benefits will be described in more throughoutthe present specification and more particularly below.

Various additional objects, features and advantages of the presentinvention can be more fully appreciated with reference to the detaileddescription and accompanying drawings that follow.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram that illustrates the general architecture of aspatial light modulator (SLM) 100 according to an embodiment of theinvention.

FIG. 2A is a simplified exploded perspective view of a micro-mirrorfabricated according to an embodiment of the present invention.

FIG. 2B is a simplified perspective view of a mirror substrate accordingto an embodiment of the present invention.

FIG. 2C is a simplified perspective illustration of a standoff structureat an intermediate stage of processing according to an embodiment of thepresent invention.

FIGS. 3A and 3B are simplified side-view illustrations of a portion of aspatial light modulator according to an embodiment of the presentinvention.

FIG. 4 is a simplified perspective view of a spatial light modulatorarray including an array of micro-mirrors according to an embodiment ofthe present invention.

FIGS. 5A and 5B are simplified schematic illustrations of an electrodesubstrate at various stages of a fabrication process according to anembodiment of the present invention.

FIGS. 6A-6G are simplified schematic illustrations of an spatial lightmodulator at various stages of a fabrication process according to anembodiment of the present invention.

FIG. 6H is a simplified top-view illustration of a spatial lightmodulator according to an embodiment of the present invention.

FIG. 7 is a simplified flowchart illustrating one method of fabricatinga spatial light modulator according to an embodiment of the presentinvention.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

According to the present invention, techniques for manufacturing objectsare provided. More particularly, the invention relates to a method andstructure for fabricating a spatial light modulator with a co-planarsurface and torsion device. Merely by way of example, the invention hasbeen applied to the formation of a spatial light modulator having atorsion spring and mirror plate positioned in the same plane. The methodand device can be applied to spatial light modulators as well as otherdevices, for example, micro-electromechanical sensors, detectors, anddisplays.

FIG. 1 is a diagram that illustrates the general architecture of aspatial light modulator (SLM) 100. The illustrated embodiment has threelayers. The first layer is a mirror array 103 that has a plurality ofdeflectable micro-mirrors 202. In a preferred embodiment, themicro-mirror array 103 is fabricated from a first substrate 105 that isa single material, such as single crystal silicon. An example of one wayof forming this SLM is described in U.S. patent application Ser. No.10/378,056, filed Feb. 27, 2003, commonly owned, and hereby incorporatedby reference for all purposes.

The second layer is an electrode array 104 with a plurality ofelectrodes 126 for controlling the micro-mirrors 202. Each electrode 126is associated with a micro-mirror 202 and controls the deflection ofthat micro-mirror 202. Addressing circuitry allows selection of a singleelectrode 126 for control of the particular micro-mirror 202 associatedwith that electrode 126.

The third layer is a layer of control circuitry 106. This controlcircuitry 106 has addressing circuitry, which allows the controlcircuitry 106 to control a voltage applied to selected electrodes 126.This allows the control circuitry 106 to control the deflections of themirrors 202 in the mirror array 103 via the electrodes 126. Typically,the control circuitry 106 also includes a display control 108, linememory buffers 110, a pulse width modulation array 112, and inputs forvideo signals 120 and graphics signals 122. A microcontroller 114,optics control circuitry 116, and a flash memory 118 may be externalcomponents connected to the control circuitry 106, or may be included inthe control circuitry 106 in some embodiments. In various embodiments,some of the above listed parts of the control circuitry 106 may beabsent, may be on a separate substrate and connected to the controlcircuitry 106, or other additional components may be present as part ofthe control circuitry 106 or connected to the control circuitry 106.

In an embodiment according to the present invention, both the secondlayer 104 and the third layer 106 are fabricated using semiconductorfabrication technology on a single second substrate 107. That is, thesecond layer 104 is not necessarily separate and above the third layer106. Rather, the term “layer” is an aid for conceptualizing differentparts of the spatial light modulator 100. For example, in oneembodiment, both the second layer 104 of electrodes is fabricated on topof the third layer of control circuitry 106, both fabricated on a singlesecond substrate 107. That is, the electrodes 126, as well as thedisplay control 108, line memory buffers 110, and the pulse widthmodulation array 112 are all fabricated on a single substrate in oneembodiment. Integration of several functional components of the controlcircuitry 106 on the same substrate provides an advantage of improveddata transfer rate over conventional spatial light modulators, whichhave the display control 108 line memory buffers 110, and the pulsewidth modulation array 112 fabricated on a separate substrate. Further,fabricating the second layer of the electrode array 104 and the thirdlayer of the control circuitry 106 on a single substrate 107 providesthe advantage of simple and cheap fabrication, and a compact finalproduct. After the layers 103, 104, and 106 are fabricated, they arebonded together to form the SLM 100. Additional examples of methods forjoining the substrates to form a bonded substrate structure aredescribed in U.S. patent application Ser. No. 10/756,923, filed Jan. 13,2004, commonly owned, and hereby incorporated by reference for allpurposes.

As illustrated in FIG. 1, the substrate 105 includes a number ofstandoff regions extending from a lower portion of the substrate andarranged in an array as a waffle pack grid pattern. The standoff regionsare adapted to align with bonding areas located between adjacentelectrodes 126. Mirrors 202 are formed in the upper layers of substrate105 by a release process in later stages of processing. In some designs,the standoff regions provide mechanical support for the mirror structureand are not moveable. Thus, light reflected from the upper surfaces ofthe standoff structures reduces the contrast of the optical systemincorporating the spatial light modulator. In some designs, an absorbentmaterial may be applied to the upper surfaces of the standoff regions toreduce reflections. However, these approaches reduce the fill factor ofthe array, potentially degrading system performance.

FIG. 2A is a simplified exploded perspective view of a micro-mirrorfabricated according to one embodiment of the present invention. Thisdiagram is merely an example, which should not unduly limit the scope ofthe claims herein. One of ordinary skill in the art would recognize manyvariations, modifications, and alternatives. As illustrated in FIG. 2A,a portion of CMOS substrate 310 includes electrodes 312, landing pads314, and bonding surface 520. Standoff structure 645 includes anintegrated surface 210 coupled to the lower surface (not shown) of themirror layer 640 and a bonding surface (not shown) opposite theintegrated surface 210. The standoff structure 645 also includescentrally located base section 650 extending from the integrated surfaceto the bonding surface along a first axis and lateral extension arms 642extending from the base section along a second axis orthogonal to thefirst axis. As further illustrated in FIG. 2A, the first axis is alignedwith the z-axis and the extension arms extend from the base sectionalong the x-axis. Of course, this arrangement is not required by thepresent invention. One of ordinary skill in the art would recognize manyvariations, modifications, and alternatives.

Referring to FIG. 2A, a torsion beam is defined in the mirror layer 640by openings 690 along with openings 682 a and 682 b. In an embodiment ofthe present invention, the torsion beam includes two torsion spring arms684 a and 684 b that extend away from two sides of central base section686. As illustrated, the torsion spring arms are coplanar with themirror layer 640 and extend along the x-axis. Each of the torsion springarms are fixed to the central base section and the mirror plate at thediagonal corners of the mirror plate. Accordingly, the mirror layer 640is free to rotate in the y-z plane in response to activation of theelectrodes 312. As the mirror layer rotates about the x-axis, arestoring torque is present in the torsion beam. Of course, thisgeometry is only one of a number of geometries provided by embodimentsof the present invention.

FIG. 2B is a simplified perspective view of a mirror substrate accordingto an embodiment of the present invention. As illustrated in FIG. 2B,mirror layer 640 has been inverted and electrode substrate 310 has beenomitted, showing the bonding surface 220 of the standoff structure 645and the underside of mirror layer 640. As will be described more fullybelow, the mirror substrate including the mirror layer 640 and thestandoff structure 645 is wafer bonded to substrate 310 in a specificembodiment of the present invention. Referring to the illustrationprovided in FIG. 2B, bonding surface 220 extends along the entire faceof the standoff structure and is bonded to bonding surface 520 usingtechniques described more fully below. Subsequently, mirror layer 640and standoff structure 645 are preferentially etched from the upper sideof the mirror layer to form openings 690 and remove the support providedby standoff structure 645 for portions of the mirror layer 640.

As described with reference to FIG. 6B below, a layer of a compositesubstrate structure is processed to form the standoff structure 645. Inthe illustrated embodiment, the standoff structure is fabricated usingan etching process that terminates at the underside of layer 640. Asillustrated, extension arms 642 extend from opposite sides of centralsection 650. In particular, adjacent arms 242 and 244 are separated byopenings 240. The dimensions of the standoff structure, in particularthe height to which the structure extends from layer 640, the dimensionsof central section 650, the width and length of the extension arms, andthe spacing 240 between the arms are predetermined according toembodiments of the present invention.

FIG. 2C is a simplified perspective illustration of a standoff structureat an intermediate stage of processing according to an embodiment of thepresent invention. In the embodiment of the present inventionillustrated in FIG. 2C, the standoff structure includes a releasesection 260 that is removed during a release step. Additional details ofthe fabrication process are discussed below. Initially integrally formedwith the mirror layer, the release section 260 includes portionsextending along both sets of extension arms 642. The thickness 262 ofthe release section is defined during the release step and is typicallya function of the etch process used to remove the release section, asdescribed more fully below. In some embodiments, the thickness 262 isselected to ensure that the mirror plate does not make contact with theextension arms 642 when the mirror is placed in an activated state. Asillustrated in FIG. 2C, the upper surface 220 of the standoff structure,which is an integrated layer coupled to the mirror layer, has a smallersurface area than the lower surface 270 of the standoff structure, whichis bonded to the second substrate as described more fully below. Asillustrated in FIG. 2C, the lower surface area of the standoff structureis equal to the surface area of the extension arms plus the surface areaof the surface 830.

In some embodiments the strength of the bond per unit area between thestandoff structure and the second substrate is less than the strength ofthe bond between layer 220 and the mirror due to the integrated natureof the interface. However, because of the ratio of areas betweensurfaces 220 and 270, the total strength of the bond and material arebalanced and may be equal or different. For example, the presence ofvoids between surface 270 and the electrode substrate is counteracted bythe bond area provided by the extension arms 642.

FIGS. 3A-3B are simplified side-view illustrations of a portion of aspatial light modulator according to an embodiment of the presentinvention. As illustrated in FIG. 3A, a micro-mirror 320 issymmetrically located with respect to standoff structure 330 and isillustrated in an unactivated position. Portions of additionalmicro-mirrors 322 and 324 are illustrated on opposite sides ofmicro-mirror 320. Electrode substrate 310 is illustrated in the figureand is typically a CMOS substrate. In a particular embodiment, substrate310 includes complementary electrodes 312 a and 312 b, as well asdisplay control, line memory buffers, and the pulse width modulationarray circuitry (not shown) as described above. In a specificembodiment, electrodes 312 are fabricated from a number of materialsthat conduct electricity and are referred to as control electrodesbecause they are used to control the deflection of the mirrorsassociated with the electrodes. Merely by way of example, the controlelectrodes in the embodiment according to the present inventionillustrated in FIGS. 3A and 3B are made of a multi-layer stack of metalspreferentially deposited on the surface of substrate 310. Preferably,the electrode is made of a deposited titanium nitride (TiN) layer, adeposited aluminum layer, and a second deposited TiN layer. Inalternative embodiments according to the present invention, theelectrodes are made of tungsten or other suitable conductors. Thethickness of the electrode stack making up electrodes 312 in oneembodiment is 8,000 Å.

In addition to the formation of control electrodes 312 on the surface ofsubstrate 310, landing pads 314 are formed in embodiments of the presentinvention. In a specific embodiment, the landing pads 314 a and 314 balso serve as bias electrodes and are formed during the same fabricationprocesses as the control electrodes. For example, in one embodiment, thelanding pads/bias electrodes are made of a multi-layer stack of metalspreferentially deposited on the surface of substrate 310. Preferably,the landing pad is made of a deposited titanium nitride (TiN) layer, adeposited aluminum layer, and a second deposited TiN layer. Inalternative embodiments according to the present invention, the landingpads/bias electrodes 314 are made of tungsten or other suitableconductors.

Moreover, FIG. 3A illustrates support pad 316. In a specific embodiment,a number of support pads 316 are fabricated on substrate 310 and alsoserve as bias electrodes. In some embodiments, the support pads 316 areformed during the same fabrication processes as the control electrodes.For example, in an embodiment, the support pads 316 are made of amulti-layer stack of metals preferentially deposited on the surface ofsubstrate 310. Preferably, the support pads 316 are made of a depositedtitanium nitride (TiN) layer, a deposited aluminum layer, and a seconddeposited TiN layer. In alternative embodiments according to the presentinvention, the support pads 316 are made of tungsten or other suitableconductors. In some embodiments, the support pads 316 are coupled to abias grid (not shown).

Micro-mirror 320 is attached to standoff structure 330 a by torsionspring hinge and the standoff structure is coupled to the substrate 310.In the embodiment illustrated in FIG. 3, a portion of the upper surface326 of the micro-mirror is a reflective surface. For example, the powerreflectance of portions of upper surface 326 may be greater than orequal to 90%. Moreover, in an embodiment according to the presentinvention, the flexible member is a vertical torsion spring, in whichthe height of the hinge is greater than the width, but this is notrequired by the present invention. Alternative embodiments according tothe present invention use other flexible members that bend in responseto applied forces and subsequently return to their original shape afterremoval of such applied forces.

FIG. 3B illustrates a micro-mirror 320 in an activated position. In thestate illustrated in FIG. 3B, a voltage V_(A) has been applied to theelectrode 312, deflecting the left side of the moveable structure awayfrom the electrode and creating a restoring counter-clockwise torque inthe torsion spring. In FIG. 3, the torque lies in the plane of thefigure. In an embodiment according to the present invention, at leastone landing pad 314 b is adapted to make contact with the micro-mirrorat location 340. The landing pad is fabricated from suitable materialsas described above.

As illustrated in FIG. 3B, the right side of the micro-mirror makescontact with landing pad 314 b. However, this is not required by thepresent invention. An example of one way of utilizing landing pads andlanding posts to reduce the amount and impact of contact between themicro-mirror and the first surface is described in U.S. patentapplication Ser. No. 10/718,482, filed Nov. 19, 2003, commonly owned,and hereby incorporated by reference for all purposes. Moreover, inalternative embodiments, the electrodes may be elevated to otherpredetermined distances above the first surface, reducing the distancebetween the electrodes and the micro-mirror, and thereby increasing theelectrostatic forces resulting from the application of voltages to theelectrodes.

Although FIGS. 3A and 3B illustrate a micro-mirror transitioning betweenan unactivated (horizontal) state and an activated (tilted) state, thisis not required by the present invention. In alternative embodiments,the micro-mirror transitions between states in which the mirror istilted in opposite directions. In embodiments according to the presentinvention, the height and position of the standoff structure areselected so that the upper surface of the micro-mirror is tilted at apredetermined angle with respect to the horizontal when the micro-mirroris in the activated state. For example, the mirror may transition from astate in which the micro-mirror is tilted at 12° to the horizontal asillustrated in FIG. 3B and a state in which the micro-mirror is tiltedat an angle of −12° to the horizontal. In these alternative embodiments,the increase in available tilt angle provides for improvements in systemcontrast when the micro-mirror array is integrated into a projectiondisplay system.

In some embodiments of the present invention, the landing pads areformed from other materials selected for such properties as electricalconductivity and mechanical rigidity. For example, in an embodiment, thelanding pads are formed from tungsten. In other embodiments, othermaterials, including polysilicon and aluminum are used to form thelanding pads. Of course, one of ordinary skill in the art wouldrecognize many variations, modifications, and alternatives.

Comparison of FIGS. 1 and 3 will illustrate one of the benefits providedby embodiments of the present invention. Since the spatial lightmodulator in FIG. 3 is centrally supported by standoff structure 330,rather than a waffle pack grid structure surrounding micro-mirrors 320,the fill factor of an array of spatial light modulators fabricatedaccording to embodiments of the present invention, which is a functionof the gap between adjacent micro-mirrors, can be higher than in somealternative designs. In embodiments in which the openings 680 a and 680b are defined using well developed photolithographic processes, thedimensions of the openings are generally well-controlled and may be assmall as sub-micron dimensions. Accordingly, high fill factors areavailable using embodiments of the present invention.

FIG. 4 is a simplified perspective view of a spatial light modulatorincluding an array of micro-mirrors according to an embodiment of thepresent invention. As illustrated in FIG. 4, a number of micro-mirrorsare arranged in a spatial pattern to form a two-dimensional array. Themicro-mirrors, supported by the standoff structures and torsion springhinges as described above, are laterally separated by air gaps 410. Forpurposes of clarity, FIG. 4 provides an illustration in which portionsof the spatial light modulator are omitted as a function of position toillustrate the three-dimensional nature of the spatial light modulatoraccording to embodiments of the present invention.

As described above, because the air gaps between adjacent mirrors areformed using photolithograph processes, the spacing between adjacentmirrors is a predetermined distance. For example, in an embodiment, theair gap 410 is 0.8 μm. In other embodiments, the air gap 410 ranges fromabout 0.3 μm to about 1.0 μm. Of course, the particular air gap willdepend on the particular application and may not be the same on allsides of a particular micro-mirror. The fill-factor of a micro-mirrorarray, defined as the area of the reflective surfaces divided by thetotal area of the array, increases as the gap between adjacentmicro-mirrors decreases. In display applications, increases infill-factor typically result in improvement in the image qualityproduced by the spatial light modulator. Thus, embodiments of thepresent invention provide photolithographically defined spacings betweenmirrors and controllable fill-factors.

FIGS. 5 and 6 are simplified schematic illustrations of a spatial lightmodulator at various stages of a fabrication process according to anembodiment of the present invention. FIG. 5A illustrates the formationof layer 510 on substrate 310. In an embodiment, the layer 510 is adielectric layer suitable for formation of dielectric bond pads 520 asillustrated in FIG. 5B and described below. In the embodimentillustrated in FIG. 5A, a 5,000 Å layer of silicon dioxide is depositedon substrate 310 and subsequently patterned to form the dielectric bondpads 520, but this is not required by the present invention. Othersuitable materials that provide a contact region suitable for bonding ofsubstrate 310 to another substrate is utilized in alternativeembodiments. Alternative embodiments utilize deposited and patternedlayers of silicon nitride, silicon oxynitride, spin-on-glass (SOG),low-k dielectrics, or the like. Moreover, dielectric bond pads 520 maybe formed by a combination of such layers.

Preferably, a dielectric layer is deposited by a low temperature processthat preserves the integrity of the control circuitry and electrodesfabricated on substrate 310 in previous processing steps. For example, alow temperature plasma enhanced chemical vapor deposition (PECVD)process is used in one embodiment to deposit a dielectric layer coveringsubstrate 310. Alternative embodiments employ atmospheric or lowpressure chemical vapor deposition (CVD) process to form the dielectriclayer. The dielectric layer may be planarized after deposition, forexample, by using a chemical mechanical polishing (CMP) process to forma uniform upper dielectric surface for the layer from which thedielectric bond pads are formed. Planarization processes for dielectriclayers utilized in multilevel interconnect applications are well knownto one of skill in the art.

After deposition of one or more dielectric layers and optional polishingsteps, a photoresist layer (not shown) is deposited on the dielectriclayer or layers. The photoresist layer is utilized in patterning of thedielectric through etching or other techniques to form the dielectricbond pads 520 illustrated in FIG. 5B. As illustrated in FIG. 5B, thedeposited dielectric layer utilized to form the dielectric bond pads 520is removed from all portions of the substrate 310 other than where thebond pads are present, but this is not required by the presentinvention. In alternative embodiments, portions of the dielectric layerremain on the substrate 310 and cover control electrodes 312 to providepassivation benefits. In embodiments in which CMP processes are utilizedto planarize the deposited dielectric layer, the upper surfaces 530 ofbond pads 520 provide an extremely smooth surface suitable for bondingto portions of substrate layer 610 as described more fully below.

In alternative embodiments, support pads 316 as illustrated in FIG. 5Aare not utilized and the layer 510 makes contact with substrate 310 atthe locations where support pads 316 are illustrated in FIGS. 5A and 5B.In these embodiments, the height of the bond pad 520 is defined by thethickness of the dielectric layer or layers 510 as deposited andplanarized as described above.

In a particular embodiment of the present invention, the geometry of thebond pads 520 formed on the electrode substrate (i.e. the CMOSsubstrate) are selected to correspond to the geometry of the standoffstructures formed on the mirror substrate illustrated in FIG. 6 anddescribed below. Thus, in this particular embodiment, the geometry ofthe bond pads 520 is a rectangular parallelepiped defined by a length, awidth, and a height. The length of the bond pad 520 illustrated in FIG.2A extends along the x-axis. In an embodiment, the dimensions of themicro-mirror 640 are approximately 15 μm by 15 μm on a side and thelength of the bond pad 520 measured in the x-direction is approximately20 μm. The width of the bond pad 520 measured in the y-direction is apredetermined width. In a specific embodiment, the width isapproximately 2 μm. In other embodiments, the width ranges from about 1μm to about 3 μm. Of course the dimensions of the length and width ofthe bond pads 520 will depend on the particular application.

FIGS. 6A-6G are simplified schematic illustrations of a spatial lightmodulator at various stages of a fabrication process according to anembodiment of the present invention. As illustrated in FIG. 6A,multi-layer substrate structure 610 includes handling layer 615,insulating layer 620, and device layer 630. In some embodiments, themulti-layer substrate 610 is referred to as a mirror substrate sincemirror layers are formed from a portion of the multi-layer or compositesubstrate. In a particular embodiment, composite substrate 610 is asilicon-on-insulator (SOI) substrate including a silicon layer 615, asilicon dioxide layer 620 (buried oxide layer), and an additionalsilicon layer 630. In alternative embodiments, the insulating layercomprises a silicon nitride layer or a composite oxide/nitride layer.Also illustrated in FIG. 6A is CMOS substrate 310, prepared as discussedin relation to FIG. 5.

In FIG. 6B, device layer 630 has been processed to form standoffstructures 645 including face 644. Prior to the processing step, face644 was the lower surface of layer 630. Although the side view presentedin FIG. 6B does not provide an illustration of the extension arms 642,reference to FIG. 2B will illustrate the extension arms 642 extending inopposite directions from centrally located base section. Of course, anumber of standoff structures, arranged in a spatial pattern as an arrayare fabricated simultaneously according to embodiments of the presentinvention. Referring to FIGS. 2B and 6B, dashed rectangle 622 representsthe spacing 240 between lateral extension arms 242 and 244 extending toone side of the centrally located base section 650.

Standard photolithography techniques can be used to generate a patternedmask layer. Typically, the mask layer, such as silicon oxide, isdeposited on device layer 630. The mask layer is then patterned to formthe mask used in the process of forming the standoff structures. Themask layer is typically characterized by a two-dimensional pattern inthe plane of the device layer. The mask layer defines regions of thedevice layer that will be etched during a subsequent etching process orseries of etching processes, forming standoff structures 645. The etchprocesses utilized will form standoff structures with predeterminedprofiles and heights.

In an embodiment, the device layer 630 is etched in a reactive ion etchchamber flowing with SF₆, HBr, and oxygen gases at flow rates of 100sccm, 50 sccm, and 10 sccm respectively. The operating pressure is inthe range of 10 to 50 mTorr, the bias power is 60 W, and the sourcepower is 300 W. In another embodiment, the device layer 630 is etched ina reactive ion etch chamber flowing with Cl₂, HBr, and oxygen gases atflow rates of 100 sccm, 50 sccm, and 10 sccm, respectively. In theseembodiments, the etch processes stop when the height of the standoffstructure, measured perpendicular to the device layer is about 1.5 μm.In alternative embodiments, the height of the standoff structure rangesfrom about 0.8 μm to about 3.0 μm. The height will depend on theparticular applications. Generally, this height is typically measuredusing in-situ etch depth monitoring, such as in-situ opticalinterferometer techniques, or by timing the etch rate.

In another embodiment, the standoff structures are formed in the devicelayer 630 by an anisotropic reactive ion etch process. The substrate isplaced in a reaction chamber. SF₆, HBr, and oxygen gases are introducedinto the reaction chamber at a total flow rate of 100 sccm, 50 sccm, and20 sccm, respectively. A bias power setting of 50 W and a source powerof 150 W are used at a pressure of 50 mTorr for approximately 5 minutes.The substrate is then cooled with a backside helium gas flow of 20 sccmat a pressure of 1 mTorr. In one particular embodiment, the etchprocesses stop when the height of the standoff structure, measuredperpendicular to the device layer is about 1.5 μm. Generally, thisheight is measured using in-situ etch depth monitoring, such as in-situoptical interferometer techniques, or by timing the etch rate.

As will be appreciated by reference to FIG. 2B, the geometry of thestandoff structures approximates the letter “H” when viewed along thez-direction. The dimensions of the outer periphery of the standoffstructure 645 is generally selected to correspond to the dimensions ofthe bond pads 520. For example, in embodiments, in which the length andwidth of the bond pad 520 are (not 20) 14 μm and 2 μm respectively, thelength and width of the standoff structure are also 14 μm and 0.4 μm. Inalternative embodiments, the dimensions of the standoff structures 645are selected to provide a margin of unbonded material at the edges ofbond pads 520. One of ordinary skill in the art would recognize manyvariations, modifications, and alternatives.

FIG. 6C illustrates the joining of substrates 610 and 310 to form acomposite substrate structure. Alignment of the substrates prior tobonding is performed according to processes well known to one of skillin the art. In a particular embodiment, the bonding surface 644 ofstandoff structures 645 is a polished single crystal silicon surface.Wafer bonding techniques are used in some embodiments to form a hermeticseal between bonding surface 644 and bonding surface 530 of bond pads520. For example, bonding may be accomplished through the use of anodic,eutectic, fusion, covalent, glass frit, and other bonding techniques. Inembodiments in which bond pads 520 and standoff regions 645 are silicondioxide and silicon, respectively, room temperature covalent bondingtechniques are used to form a hermetically sealed bond between thestructures. In embodiments in which standoff regions 645 and bond pads520 are silicon, room temperature covalent bonding techniques are usedto form a hermetically sealed bond between the substrates. Of course,one of ordinary skill in the art would recognize many variations,modifications, and alternatives.

In some embodiments, substrate 610 initially includes multiple layersfor structural support and to provide benefits during processing. Inthese embodiments, upper layers 615 and 620 of substrate 610 are removedin a subsequent processing step, as illustrated in FIG. 6D. In order tothin substrate 610 after bonding, thinning processes using chemicalmechanical polishing (CMP), grinding, etch back, any combination ofthese, and the like are used. In one application, the buried oxide layer620 provides an etch stop layer during the thinning process. In aparticular embodiment, after these layer removal and/or polishing steps,the thickness of the layer 640 is 0.3 μm. Therefore, the thickness ofthe layer 640 is selected to optimize design constraints for themicro-mirror devices, including structural rigidity, flexibility, andamount of inertia. Moreover, as described more fully below, otherportions of layer 640 are processed to form torsion spring hingescoplanar with the mirror layer. Thus, the thickness of the layer 640 isalso selected to optimize design constraints for the torsion springhinges.

FIG. 6E illustrates a spatial light modulator at another stage of afabrication process according to an embodiment of the present invention.As illustrated in FIG. 6E, openings 660 have been made in layer 640 oflayer 640, as well as through central portions of standoff structure 645and dielectric bond pads 520. In an embodiment, a photoresist layer isdeposited on the upper surface of layer 640, patterned and used as anetch mask to etch openings 660 through layer 640 and structures 645 and520. In a specific embodiment, the etch process is terminated at thelower surface of dielectric bond pads 520 when the TiN layer present onlayer 316 is reached. Etch chemistry that is selective for silicon andsilicon dioxide over TiN is well known to one of skill in the art. Asillustrated in the figure, an anisotropic etch that produces straightside walls for feature 660 is used in some embodiments, although this isnot required by the present invention. In alternative embodiments, otheretch processes that produce openings of sufficient size and profile areutilized.

FIG. 6F illustrates a spatial light modulator at yet another stage of afabrication process according to an embodiment of the present invention.As illustrated in the figure, at least one layer of material 664 hasbeen deposited on the layer 640 and in openings 660. In some embodimentsof the present invention, the deposited material is able to both conductelectricity and reflect optical radiation. In a particular embodiment,the material 664 is a multi-layer stack of metals preferentiallydeposited on the surface of layer 640 and in openings 660. Preferably,the material 664 and 665 is made of a deposited TiN layer and adeposited aluminum layer. For example, in a specific embodiment, the TiNlayer is 150 Å thick and the aluminum layer is 300 Å thick. Inalternative embodiments according to the present invention, thethickness and composition of the deposited layer or layers of material664 is varied, utilizing other materials that conduct electricity andreflect light in the visible region.

As illustrated in FIG. 6F, multi-layer stack 664 provides a reflectivecoating on the upper surface of layer 640. As described more fullybelow, portions of layer 640 are processed to form micro-mirrors, whichreflect light incident from above layer 640. Thus, the upper layer ofstack 664 illustrated in FIG. 6F, which includes an aluminum layer,provides a high reflectivity coating for the mirror surface suitable forreflecting incident radiation in the visible region.

Moreover, since the deposited material passes through insulatingdielectric layer 520, layer 665 provides for electrical connectionbetween the mirrors formed in portions of layer 640 and a bias grid (notshown) coupled to support pads 316. As illustrated in FIG. 6F, material665 and support pads 316 are coupled at the upper surface of the TiNlayer deposited as the upper portion of support pads 316. Thus,structures 664 and 665 provide not only a reflective coating on theupper surface of layer 640, but also provide for an electricalconnection between the mirror surface and the bias grid.

In some embodiments, the bias grid is present on the same masking levelas the electrodes 312 and support pads 316. In alternative embodiments,the bias grid is present on another level, for example, the same maskinglevel as metals deposited and patterned prior to electrodes 312 andsupport pads 316. In these alternative embodiments, the bias grid iselectrically connected to the support pads 316 through the use of vias,reducing the number of physical structures present at the electrodesmasking level and simplifying the electrical design. One of ordinaryskill in the art would recognize many variations, modifications, andalternatives. As the structure 664 is present on the upper surface ofthe hinges extending toward the corners of the micro-mirror, themulti-layer stack provides electrical connectivity between the bias gridand the entire mirror surface. Semiconductor processing techniquessuitable for enhancing the electrical contact between the conductivelayer 664/665 and the support pads 316 are well known to one of skill inthe art, including plasma treatment after formation of openings 660 andprior to deposition of the first layer making up the multi-layer stack664/665.

Although in some embodiments, layers 664 and 665 are distinguishable, inother embodiments, a single reflective and conductive material is usedboth to fill the openings 645 and coat the surface of layer 640.Moreover, in some embodiments, the material 665 does not completely fillthe openings 645, but still provides a continuous electrical path fromthe bias grid to the layer 664.

FIG. 6G illustrates a spatial light modulator at a further stage of afabrication process according to an embodiment of the present invention.As illustrated, layer 640 has been patterned using photolithographicprocesses and processed to form a number of openings 680 a, 680 b, 682a, and 682 b, creating a number of micro-mirrors 670. Although FIG. 6Gillustrates a cross-sectional view of the mirror structures, one ofordinary skill in the art will appreciate that a three-dimensionalstructure is represented by the figure. Openings 680 provide forseparation between adjacent micro-mirrors. As discussed in relation toFIG. 4, the fill-factor for the micro-mirror array is a function of thegap between adjacent mirrors. Because the openings 680 are defined usingwell developed photolithographic processes, the dimensions of theopenings are generally well-controlled and may be as small as sub-microndimensions. Openings 680 separate adjacent mirrors from each other,enabling for mirror rotation as described below.

Also illustrated in FIG. 6G and FIG. 6H are openings 682 a and 682 bformed in layer 640. Openings 682 partially define a torsion springhinge along section 684 of micro-mirror 670. As shown in FIG. 2A,openings 680 cooperate with openings 690 to form a torsion beam coupledto mirror layer 640. As illustrated in FIG. 6H, the torsion beam,sometimes referred to as a torsion spring hinge, couples themicro-mirrors 670 to a central portion of standoff structure 645. In aspecific embodiment, the openings 682 and 690 are formed in layer 640and selected portions of standoff structures 645 to release themicro-mirror in a manner to allow for rotation of the mirror around anaxis. Referring to both FIG. 6H and FIG. 2A, portions of the extensionarms 642 initially coupled to the mirror surface at locations 690 areremoved during the release process. In other words, sections 690 of themirror layer are removed along with attached sections of the extensionarms, exposing surfaces 692 on the extension arms. In the embodimentillustrated in FIG. 6H, the width of the torsion spring 684 measuredalong a direction (the y-direction) perpendicular to the length of thehinge (the z-direction) is a predetermined distance. In one specificembodiment, the width of the torsion spring hinge is 0.18 μm. In analternative embodiment, the width ranges from about 0.1 μm to about 0.5μm. The thickness of the torsion beam, measured in the z-direction, isequal to the thickness of layer 640 as illustrated in FIG. 6D.

As a result of the fabrication process described in relation to thisembodiment, the centrally located base section extends to a greaterz-height than the extension arms as illustrated in FIG. 2A. Thus, inthis embodiment, the mirror layer 640 and the standoff structure 645 arein contact at the centrally located base section 210 while othersections of the upper portion of the standoff structure (namely theextension arms) have been removed. The removal process is performed toprovide sufficient clearance between the upper portions 692 of thestandoff structure and the mirror layer 640 for the mirror to rotatefreely under the influence of an applied electric field and placed in anactivated state. In the activated state, the torsion force present inthe torsion beam provides a restoring force to return the mirror to theunactivated state after removal of the applied electric field. Moreover,because of the spacer (reference numeral 240 in FIG. 2B and referencenumeral 622 in FIG. 6B) formed between adjacent extension arms, themajority of section 684 of the torsion beam is not coupled to thestandoff structure, but functions as a torsion spring for mirror 670.

The standoff structures employed in embodiments of the present inventionprovide a mounting surface for the micro-mirror with material propertiesand dimensions that facilitate bonding of substrates 310 and 610. Insome substrate bonding processes, voids are formed at the bondinterface, weakening the bond and presenting reliability problems.Embodiments of the present invention reduce the adverse impacts of voidspossibly formed at the bond interface. For example, referring to FIG.2B, the interface between the mirror layer 640 and the standoffstructure 645 is fabricated from a single piece of material in theillustrated embodiment. In a particular embodiment, the interfacebetween the mirror layer 640 and the standoff structure 645 isfabricated from a single crystal silicon substrate. Typically, thesingle crystal silicon substrate is formed as the substrate is cut froma boule or through an epitaxial process, providing a continuous materialinterface characterized by uniformity at the interface. For thisinterface, the void density is typically zero as a result of thesubstrate fabrication processes. Accordingly, the mechanical propertiesof the material at the interface between the mirror layer and thestandoff structure, including the interface strength, are optimal.

Referring once again to FIGS. 2A and 2B, the characteristics of theinterface between the standoff structure 645 and the bond pad 520 are afunction of the substrate bonding process (or processes) used to jointhe substrates and form the composite substrate structure. Generally,the substrate bonding process is selected to reduce the number of voidsformed at the bond interface. However, in embodiments of the presentinvention, the dimensions of the lower portions of the standoffstructure provide a robust bond, even in the presence of some voids. Asillustrated in FIGS. 2A and 2B, the outer dimensions of the lowerportion of the standoff structure are approximately 14 μm by 2 μm. Inparticular, the dimensions of the extension arms 642 are approximately14 μm by 0.6 μm, providing a bonding surface that is able to tolerate anumber of voids without significant impact on interface strength andreliability.

Moreover, the geometry of the standoff structure and torsion springhinge are not limited to the geometry illustrated in FIG. 2. Inalternative embodiments of the present invention, the shape anddimensions of the standoff structure and torsion spring hinge aremodified as appropriate to other applications. In some embodiments, thewidth of the extension arms 642 are increased to provide additionalsurface area for the substrate bonding process, thereby increasing thereliability of the bond between the standoff structure and the secondsubstrate. In other embodiments, the width and length of the centrallylocated base section is increased to increase the surface area of theintegrated interface between the upper portion of the standoff structureand the mirror layer. Furthermore, the dimensions of the torsion springhinge are variable and may be selected to achieve system goals such asflexibility and reliability of the hinge.

FIG. 7 is a simplified flowchart illustrating one method of fabricatinga spatial light modulator according to an embodiment of the presentinvention. Process 700 includes providing a first substrate having amirror layer in step 710. As described previously, in a specificembodiment, the first substrate is a multi-layer substrate structure,such as a SOI substrate. The dimensions of the layers making up themulti-layer substrate are selected to satisfy various designconstraints. For example, in one embodiment of the present invention, asilicon layer is provided that is thick enough to form a mirror layerintegrated with a standoff structure. The surfaces of the SOI substrateare polished in some embodiments to facilitate substrate bondingprocesses in subsequent processing steps.

Step 712 includes forming a standoff structure from the first substrate.In some embodiments, the standoff structure is formed by an etchingprocess. In this embodiment, a surface of the first substrate is maskedand etched to form a standoff structure extending from the firstsubstrate. Typically, a mask is generated to define the portion of thefirst substrate that will be etched to form the standoff structures.Standard techniques, such as photolithography, can be used to generatethe mask on the first substrate. As mentioned previously, in anembodiment the micro-mirrors and standoff structures are formed from asingle material, such as single crystal silicon. The structuresfabricated to create the micro-mirrors and standoff structures aretypically larger than the features used in CMOS circuitry, so it isrelatively easy to form the micro-mirrors and standoff structures usingknown techniques for fabricating CMOS circuitry.

After the mask is generated, the first substrate is anisotropicallyetched in an embodiment to form the standoff structures. Other methodsbesides an anisotropic etch may also be used to form the standoffstructures, such as a wet etch or a plasma etch. One of ordinary skillin the art would recognize many variations, modifications, andalternatives. Because the unetched surface of the standoff structure ismasked during fabrication, this surface provides a bonding surface forsubsequent substrate bonding processes. As mentioned previously, thepolished substrate surface, present at the unetched surface of thestandoff structure, provides a high quality bonding surface.

A second substrate is provided in step 714. Typically, the secondsubstrate is an electrode substrate, e.g. a CMOS substrate, including anumber of electrodes and bond pads. In embodiments according to thepresent invention, the second substrate includes a bonding surfaceadapted to align with the standoff structures fabricated on the firstsubstrate. In some embodiments, the bonding surface is a dielectric bondpad formed in contact with the second substrate, but this is notrequired by the present invention. In other embodiments, the bondingsurface is a portion of the second substrate. The bonding surfaceassociated with the second substrate is typically polished or otherwisefabricated to provide a smooth surface suitable for substrate bondingprocesses.

In step 716, the bonding surface of the standoff structure is joined tothe bonding surface of the second substrate. The first substrate and thesecond substrate are aligned so that the electrodes on the secondsubstrate are in a proper position to control the deflection of themicro-mirrors formed in subsequent processing steps on the firstsubstrate. In an embodiment, the two substrates are optically alignedusing double focusing microscopes by aligning a pattern on the firstsubstrate with a pattern on the second substrate and the two substratesare bonded together by low temperature bonding methods such as anodic oreutectic bonding. There are many possible alternate embodiments to thebonding process illustrated by step 716. For example, thermoplastics ordielectric spin glass bonding materials may be used so that thatsubstrates are bonded thermo-mechanically.

After bonding the first and second substrate together, the surface ofthe first substrate opposite the standoff structures is thinned to apredetermined thickness in step 718. First, the handling layer 615 isremoved, typically by grinding or etching. Then the insulating layer 620is removed. Then the device layer 630 is thinned or polished, ifnecessary. This thinning is done in an embodiment by mechanicallygrinding the first substrate to a thickness that is near the desiredthickness of the micro-mirror. For example, in this embodiment, thethickness achieved by mechanical grinding is approximately 5 microns.The first substrate is then polished by mechanical fine polishing orchemical mechanical polishing to the thickness desired for themicro-mirror layer. In an embodiment according to the present invention,this desired thickness is less than approximately 1 μm. In a specificembodiment, this desired thickness is 0.3 μm.

In step 720, the first substrate is masked and processed to release aportion of the first substrate to form a torsion beam or torsion springhinge that is coplanar with the micro-mirror layer. Referring to FIGS.2A and 6H, in an embodiment, a high-aspect-ratio anisotropic etchingprocess is used to define the mirror plate 670, the torsion spring hinge684, and the centrally located base section 686. The release stepremoves a portion 682 of the mirror layer adjacent to the centrallylocated base section as well as a portion of the mirror layer 690 andthe portions of the extension arms above surface 692 of the extensionarms. Thus, the centrally located base section provides a connectorbetween the torsion spring hinge coupled to the mirror plate and thestandoff structure bonded to the second substrate. Additionally, therelease step 720 includes the separation of adjacent mirrors from eachother, represented by openings 680 in FIGS. 6G and 6H. In an embodiment,the width of release section 682 is 0.2 μm. In alternative embodiments,the width varies from about 0.1 μm to about 1.0 μm. Moreover, in someembodiments, the release sections 690 extend to about 1 μm from thecorner of the mirror.

The examples and embodiments described herein are for illustrativepurposes only. Various modifications or changes in light thereof will besuggested to persons skilled in the art and are to be included withinthe spirit and purview of this application and scope of the appendedclaims. It is not intended that the invention be limited, except asindicated by the appended claims.

1. A spatial light modulator, the spatial light modulator comprising: afirst substrate comprising a plurality of electrically activatedelectrodes and a bias grid; a standoff structure coupled to the firstsubstrate, the standoff structure comprising: a central portionprojecting to a first height above the first substrate, and an extensionportion projecting to a second height above the first substrate, thesecond height being less than the first height; and a mirror platecomprising: a central contact structure integrally formed with thecentral portion of the standoff structure, a torsion beam coplanar withthe central contact structure and free from contact with the standoffstructure, and a reflective surface coupled to the torsion beam and freefrom contact with the standoff structure.
 2. The spatial light modulatorof claim 1 wherein the central portion of the standoff structurecomprises a body section extending from the first substrate to themirror plate.
 3. The spatial light modulator of claim 2 wherein the biasgrid is electrically coupled to the mirror plate by a via passingthrough the body section of the central portion of the standoffstructure.
 4. The spatial light modulator of claim 2 wherein thestandoff structure and the mirror plate are formed from a single pieceof material.
 5. The spatial light modulator of claim 4 wherein thesingle piece of material is single crystal silicon.
 6. The spatial lightmodulator of claim 1 wherein the standoff structure is coupled to thefirst substrate by a substrate bonding process.
 7. The spatial lightmodulator of claim 1 wherein the standoff structure is coupled to thefirst substrate at a location between a pair of complementaryelectrodes.
 8. The spatial light modulator of claim 1 wherein thetorsion beam comprises a plurality of torsion arms extending in oppositedirections from the central contact structure.
 9. The spatial lightmodulator of claim 8 wherein the plurality of torsion arms extend alonga diagonal direction with respect to the mirror plate.
 10. Amicro-mirror flexibly supported by a standoff structure, themicro-mirror comprising: a mirror layer having an upper surface adaptedto reflect incident radiation and a lower surface opposite the uppersurface; a first portion of the standoff structure integrally formedwith the mirror layer comprising: a first planar interface coupled tothe lower surface of the mirror layer; a second planar interfaceopposite the first planar interface; and a body section extending alonga first axis from the first planar interface to the second planarinterface; a second portion of the standoff structure extending along asecond axis perpendicular to the first axis, the second portioncomprising: an upper surface physically separated from the plane of thefirst planar interface by a first distance; a lower surface coplanarwith the second planar interface; and a body section extending along thefirst axis; and a substrate coupled to the second planar interface ofthe first portion of the standoff structure and to the lower surface ofthe second portion of the standoff structure.
 11. The micro-mirror ofclaim 10 wherein the mirror layer and the first portion of the standoffstructure are fabricated from a single piece of material.
 12. Themicro-mirror of claim 10 wherein the upper surface of the second portionof the standoff structure is physically separated from the plane of thefirst planar interface by an etching process.
 13. The micro-mirror ofclaim 12 wherein the etching process is an anisotropic etching process.14. The micro-mirror of claim 10 wherein the mirror layer comprises acentral support region and a plurality of torsion arms coupled to thecentral support region.
 15. A method of fabricating a spatial lightmodulator, the method comprising: providing a first substrate structurecomprising a plurality of layers; forming a standoff structure in afirst layer selected from the plurality of layers of the first substratestructure; providing a second substrate comprising a bonding surface anda support surface; joining the standoff structure to the bonding surfaceof the second substrate; removing at least a second layer selected fromthe plurality of layers of the first substrate structure; selectivelypatterning the first layer of the first substrate structure to form amicro-mirror; and selectively patterning the first layer to remove aportion of the standoff structure and form a torsion spring hingeco-planar with the micro-mirror.
 16. The method of claim 15 whereinselectively patterning the first layer comprises etching the firstlayer.
 17. The method of claim 16 wherein etching comprises a dry etchprocess.
 18. The method of claim 15 wherein the first substratestructure comprises a silicon on insulator substrate.
 19. The method ofclaim 15 wherein the first layer selected from the plurality of layersof the first substrate structure is a silicon layer.
 20. The method ofclaim 15 wherein the second layer selected from the plurality of layersof the first substrate structure is an insulator layer.
 21. The methodof claim 15 wherein selectively patterning the first layer of the firstsubstrate structure to form a micro-mirror and selectively patterningthe first layer to remove a portion of the standoff structure areinitially performed simultaneously.
 22. The method of claim 15 whereinthe standoff structure is formed substantially in the shape of an “H”when viewed in a direction orthogonal to the micro-mirror.